Trunking system



E; WOCHINGER- 2,248,799

TRUNKING SYSTEM Filed Dec. 2l, 1958 July 8, -1941.

2 Sheets-Sheet l INVENTOR: EDUARD WOCHINGER ATTORNEY.

\ July 8, 1941. E, woCHlNGER 2,248,799

TRUNKING SYSTEM Filed Dec. 21, 1958 2 Sheets-Sheet 2 c/ Y c2 c3 U3 T 4o l ,00 4/a/7 42x 43,00 ,06,00

X- I' /08po /07/00 @en 109m P0 F e. 2 A o b v INVENTOR.' EDUARDl WOCHINGER ATTORNEY.

Patented July 8, 1941 UNTTED STATES PATENT orwell-3v 'die Verwaltung und Verwertung von gewerblichen Schutzrechten m. b.-H.,IBer-lin, Germany Application December 21, 1938', Serial No. 246,989

In Germany January 3`, 1938 Eduard Wochinger,

Claims.

Circuit arrangements for automatic telephone installations having several oiiices in tandem.

The invention relates to automatic telephone exchanges having several tandem oiiices in which the called stations are reached over the lines set up by preliminary selectors and in which the connecting lines forming a desired connection are selected by the transmission of dialled pulses over the junction lines to selectors.

In such installations it is immaterial Whether one or several junctions intervene between the calling and called stations so long as these lie in the desired direction.

In this connection there'are several known arrangements in which by the dialling of a designating digit the switching apparatus seized by the calling line becomes eiiective and in which through switching in the selector after it has been set in accordance with the designating digit from the calling line or in which the setting of the same by a designating digit from the calling line is prevented and a revertive switching of the connection via the call finder which has been set on the terminals of the calling line is effected. These arrangements require the Provision of a considerable amount of equipment since the normal operation of the selector is interfered with and a revertive connection at thecall finder must be undertaken.

Further, arrangements have become known in which the revertive switching, after the release of the foregoing selectors, is prevented since by dialling the designating digit the selectors are set over the calling line. Here also considerable equipment is involved which is taken up in the test circuit in order that the line from the call nder to the accompanying line selector is'V free and the remaining lines appear busy while at the same time other line selectors appear busy to the calling line.

Other arrangements have been proposed in which the setting of the selector by the calling line is, on a revertive call in the calling subgroup, made possible in that each junction line is joined to tWo contacts in the selector contact bank. In the speaking contact banks these two contacts are connected together, while in the test contact bank one of them is connected tova corresponding contact in the preselector switch and the other contact to the usual test wire to determine the condition of occupancy. If a revertive call is being set up the stoppage of the selector on the terminals of the calling line is elected by the rst contact of the test contact bank in dependence on the designating digit through the preselector, while by the setting up of other connections, the stoppage of the selectors is eected in dependence upon the usual testing process on a free line of the designated traffic direction- The present invention covers another method in which without revertive switching via the preselector apparatus, the calling line is utilized for setting up revertive calls. This is attained by making effective the control of the selectors through current pulses corresponding to the preordained exchange which permits the positioning of an auxiliary' selector in the taking route to the pre-ordained exchange by means of a preselectin'g switch controlled by the designating digit.

Figs. 1, 2A and 2B show an example of one method of carrying the invention into effect.

Fig. 1 shows a semi-automatic system chosen to` illustrate the features of the invention. It consists of three sub-orrices Ul, U2 and U3 and a main exchange HA. The sub-exchanges UI and U3 'are'in tandeml to the subexchange U2 and reach this'via the main exchange HA in which there is' an operator who effects the necessaryY connections between the subscribers of the individual sub-exchanges. In place of an operator, full automatic operation can be arranged for in the main exchange HA and a storage equipment provided there Which receives the dialled pulses from the sub-exchanges and then builds up the required connection.

Figs. 2A and 2B show the switching technicalities of the schematic diagram of Fig. 1 for the sub-office U2 and especially the two selecting means consisting of a call-finder AS and line selector LW with an auxiliary selector EW.

As can be seen from Fig. 1, in the sub-exchange UI selective means are provided of which only the call nder ASI and the line selector LWI are shown. From these two selectors connecting lines al /bl anda2/b2 branch to the sub-exchange U2 and end there in the contact banks of the call linden and line'selector (AS/LW) selector pair. To the contact banks of this pair of selectors are attached the lines coming from the sub-exchange UI and the lines from the sub-exchange U3 as well as the lines'from the individual subscribers, the dilerent groups of lines terminating in different levels of the linev selector LW.

The individual subscribers are connected to the first level while in the third level the lines to the sub-exchange U3 are connected. The junction lines are then connected to a supplementary, auxiliaryrselector EW which serves for theso-called revertive vcalling in the called sub-exchange group and on which the junction lines are connected for the purpose 'of making possible the further connection in the next sub-exchange.

From the sub-exchange U2 junction lines ao/Zno are led from the switching selector AW to the main exchange HA. Obviously the number of selector pairs in the individual sub-exchanges and the junction lines between these as well as the individual sub-exchanges and between the sub-exchange U2 and the main exchange HA can be varied according to requirements.

If a subscriber such as Tnl of sub-exchange UI in such a system calls then, first, in known manner a free call finder, say ASI is set in operation and places itself on the calling subscribers lines connecting him to the sub-exchange U2 over a junction line such as :t2/b2. This operation is now effective in the sub-exchange U2 and causes the operation of a further free call iinder such as- AS. This sets itself on the junction line`a2/b2 over which the call has been received. When AS comes to rest, a switching selector such as AW sets itself on a free junction line to the main exchange HA in readiness for thecall to the operating position there. The call signal is now received. The operator plugs in in the usual way into the jack which is indicated and replies to the calling subscriber. If the subscriber TnI has not waited for the through connection to the main exchange HA, he is called by the operator over the route which has been built up. The calling subscriber can only attain a connection through the action of the operator at the main exchange with the subscribers of any network or, after suitable adjustment of the line selector LW in the sub-exchange U2 with subscribers of this exchange or by control of the line selector LW and further control of the line selector LW2 with a subscriber of the sub-exchange U3 respectively,

or by control of the line selector LW and auxiliary selector EW and subsequent adjustment of line selector LWI with a subscriber in his own sub-exchange. In the last case the line selector LW is set by means of a designating digit to the iirst contact of a certain level to which are connected the junction lines ce2/b2 between subexcnange UI and U2. There is no hunting operation and the auxiliary selector is set in operation by means of the call finder AS reached by the designating digit and the connection is switched through to the line selector LWI.

By setting the auxiliary selector EW the possibility is offered, in cases where only one junction line is available between sub-exchanges UI and U2, to build up a revertive connection to the subexchange UI, or if several junction lines are available between these exchanges for the revertive connection to be formed over the line seized for the call and thus obviate the use of a second junction line.

This so called revertive selection in the calling sub-exchange or in the calling sub-exchange group with several tandem sub-exchanges is now described by means of Figs. 2A and 2B.

If subscriber Tnl of UI (Fig. l) calls (lifts telephone o hook operates a magnet or key, etc.) a free call finder in UI such as ASI is started which hunts to nd the calling subscriber Tnl If, at this instant, there is no free call finder, then, in known manner, the call is stored which, cn a call iinder becoming free starts this up.

After the call finder ASI has found the calling subscriber TnI, the latter is connected over the junction line L2/b2 to the sub-exchange U2. From the sub-exchange UI an alternating current impulse is sont over the wire b2 which energizes relay R through its winding I. Relay R locks up by the closure of its contact Ir and via this contact and the contact 5t. If the call iinder AS in the sub-exchange U2 is free then, by closure ol' contact I2r relay Mt is energized via: earth, battery, relay Mt, contacts IEsp, I4q, I3t, IZT, earth. By closure of contact 22mt, relay S is' energized via: earth, battery, relay S, contact 22mt, earth. Via contact I8s a circuit is closed for the rotary magnet of the call iinder. This circuit is: earth, battery, rotary magnet Das of AS, contact 20H, Igp, |83, I6sp, |49, I St, I2r, earth. The call iinder AS takes one step. By opening contact 'ldas oi the rotary magnet Das the short-circuit on winding I of relay RI is removed so that RI, in a branch to the energizing circuit of the rotary magnet Das, is energized and at its contact 20H disconnects the circuit of the rotary magnet of the call finder AS. This sets up the known to and fro operation of the rotary magnet of the call nder AS and the relay RI, so that the call finder progresses step-by-step, until it reaches the junction line z2/b2 which has been seized by the calling subscriber. In this case the following circuit is formed: earth, battery, relay T, contact 9T, It, winding II of relay R, contact IIT, wiper c of AS, windings I and II of relay P, contacts 621m, 63m, shaft contact GG'kZw of the line selector LW, earth. Relays P and T operate in this circuit while relay Ris held energized. By opening of contact 5t the call storage arrangement is disconnected while by opening contact I3t relays Mt and RI as well as the rotary magnet Das are freed from current. As a result of the opening of contact 22mt, relay S releases. In the meantime, through the energization of relay P via contacts 44p and 45p, the talking wires are switched through while, during the closure of the contact 68p, the junction line reached from the call finder AS is busied. By closure of contact 30p, relay Sp is energized which now, by the closure of contact I'Isp prepares the starting circuit for the iollowingdcall finder (not shown) so that further calls from the subscribers of the sub-exchange U2 or over the junction lines of other sub-exchanges via a second selector pair of the sub-exchange U2 can be dealt with. After energization of relay P the following circuit is closed via contact 3| 1n; earth, battery, resistance Wz'3, contact 3Ip, 32g, relay An, earth. Relay An operates in this circuit and permits by a method, not here of interest, the starting up of the switching selector AW for the purpose of connecting the selector pair AS/LW seized by the calling subscriber. The test relay PO is connected to the wiper d of the switching selector AW via contact 4 Ian so that on obtaining the designated selector pair via contact 3Isp, the following circuit is formed: earth, battery, winding II of relay G,

.contact 33g, shaft contact 34wlw of line selector LW, contact 31.91), wiper d of the switching selector AW, contact 4I an., windings I and II of the relay PO, earth. Relay G operates in this circit. At the opening of contact 32g, the relay An is deprived of current so that further stepping of the selector AW is prevented. Relay PO by short-circuiting of its high resistance winding I via its contact 40210 busies the selector pair, while by closure of contact Ilpo and Illpo, through switching over the junction line ao/ZJo takes place to the main exchange HA. In the meantime through previous closure of contact IIan at the start of the switching selector AW, alternating current is applied to the wire bo which produces a call signal atthe main exchange HA. In place of the main exchange HA a further sub-exchange can obviously be reached over the junction lines,

ao/bo in which case, in the same wayas in the sub-exchange U2, the corresponding relay R is energized by alternating. current with the same switching process for the purpose of through switching to the main exchange HA lying behind this. Whatever switching process s employed does not matter. Assuming that for the sake of simplicity that in the previous case HA has been reached over the junction lines aci/bo, then the calling, signal is produced by alternating current. The operator answers .by plugging into the jack of the calling line. As a result a circuit (not shown) is formed via the wire ao of the junction line for theA relay J which operates. By closure of contactiy', relays Cand Cl become energized and lock themselves upV by closure of Contact Stic in a holding circuit.

Ii the calling subscriber has waited then, via the loop from the subscriber, a relay corresponding to Y in the sub-exchange Ul is energized and via its contact corresponding to y and a choke coil corresponding to Dr2, places battery potential to the wire b2 by which the relay Y of sub-exchange U2 is energized via: wire b2, wiper arm b of thecall nder AS, contacts 45p, 53u, 55h, Elc, ie, relay Y, earth. Relay Y at its contact 'ly and choke coil Dr? places a battery potential on the wire 'bo of the junction line so that a signal is given to the operator at the main exchange which indicates that the subscriber has taken his telephone off thehook.

I1 the calling subscriber has not waited, this battery potential is not applied and the operator receives no signal. The operator calls the subscriber. This back calling is introduced in known manner via wire bo in sub-exchange U2 and operates relay E and from there via contact 68e is transmitted to the sub-exchange Ui from which a call is sent out. Vinen the subscriber answers calling current is cut oi. The operator answers and can set up any oi the already mentioned arrangements.

The following case is of interest for back calling connections. If, by way of example, a calling subscriber Tnl desires a subscriber in his own subexchange Ul. The operator must in this case set the line selector LW of the calling sub-exchange b-y means of the designating digit. There, as shown above, the junction linev to the sub-exchange UI- is connected to the second level of the line selector and the designating digit is 2. The operator sends two impulses. These result in the energizing circuit over the Wire ao including a relay J being twice interrupted. Contact 181 is thereby closed so that the vertical magnet of the line selector receives two current impulses via: earth, battery, vertical magnet H of LW, shaft contact 'lgwlw of LW, contacts 78j, Tlc, earth.

During the transmission of the impulses, relay V isimpulsively operated via contact 837 while the slow relay VI is continuously energized. The line selector LW has a level contact ZQdlc which is closed every time the line selector is stepped on to a level to whose contacts the junction lines are connected. This level contact is also closed in the previous case so that the following circuit is formed: earth, battery, relay Q, contact 21u, level contact 29dk of LW, earth. Relay Q energizes in this circuit and locks itself up in a holding circuit vla its contact 28:1.

If at the end of the impulse train, relay VIl releases, then, via contact 1.511: after the: first vertical step of the line selector LW, the shaft contact 'lllclw of LW is closed and .the following circuit is formed: earth,` battery, rotary magnet of D of LW, contacts Tq, 1.41ct, 13M, 7212i, shaftfcontact 'Hjclw of LW, earth. Rotary magnet D is energized in this circuit, and rotates the selector AW in on to theV first level- The rotation of LW closes. shaft contact llllwlwl so that via this contact and the contact 9811i, relay K is energized. By the closure of contact 54k, relay B is connected to the Wire b2' of the junction line from .thev sub-exchange Ul.

telephone down, battery potential is applied to the wire b2 and relay B energizes. B locks itself up over its contact 55h independently of contact. 54k. In the meantime, by opening .of contact 'llc, the current torelay Y is interrupted so that this relay also releases. A holding circuit is formed for the relay K at contact 9111. which is independent of contact 9810i.

As in the previous cases, the call nder AS is already standing on the junction. line fromY the sub-exchange UI (line (L2/b2). and by setting of the line selector LW, a connection in the same direction (revertive call) is designated then, immediately after the first step. of the line selector LW, the following circuit is formed: earth, battery, relay Tl, contact "14p, wiper d of call finder AS on contact 3,. wiper c of theV line selector LW and contactK Il of the second level, windings I and II of relay PI, 'contacts 8912i, Qilc, h, Mol, earth. Relays TI and PI are energized in this circuit. Bythe opening of Contact 14p! magnet D of LW is prevented. The following circuit is closed by the closure of contact Hltl. Rotary magnet Dew' of the auxiliary selector EW, Contact H321, ll2u, Illtl, earth. The rotary magnet Dew operates alternately with relay Rl whose winding II is influenced over contact dew of the auxiliary selector for such time until its wiper c has found the contact 3 via the wiper e of the call finder AS. If this is the case, the following circuit is formed: earth, battery, relay U, wiper e of the call nder AS, wiper c of the selector EW, contact Hlt, earth. Relay U operates in this circuit and stops the selector EW by opening the contact H211.. By closure of contacts 2u, and 3u, wipers a and b of the auxiliary selector EW are connected to the talking wires so that through switching is effected to the lines z2/b2.

After switching through contacts 45u, `and 53u are opened so that the call finder AS is disconnected.

By reason of the switching through of the connecting junction lines from the sub exchange rUl Via AS, the relay B connected to the line b2 is deprived of current. The testing circuit of the call nder AS remains closed so that the relay P is locked up.

In this way it is possible, in cases whereV the desired connection is not effected, for the operator by special means to release the line selector LW without at the same time releasing the connection which has been built up via thev call nder to the operator.

By the special means relays J and E are controlled by the operator so that the line selector LW with the auxiliary selector EW (C'and CI deenergized) are released, the call finder however is (contact 65e closed) heldin the positionin which it has been set.

Then, as. mentioned above, when the subscriber takesv hisV further operation of .the rotary The operator can then immediately set up an alternative connection Without it being necessary for the subscriber to once again set up a path to the operator.

Since, as explained above, in the course of the connection relay U is energized, then by opening of contact 21u, relay Q is released andby closure of contact. 92u .the holding circuit of relay PI is maintained independently of contact 95D.

Since' after the transmission of the iirst impulse group from the operator relay J is again continuously energized, then, via lcontact 5M' after through switching Via contacts 2u and 3u, a relay corresponding to relay J in the subexchange is operated via: earth, battery, resistance Wi2, choke coil D13, contacts 5U, 3u, wiper a of the selector EW, Wire a2 of the junction line to the sub-exchange UI, a relay corresponding to relay J, earth. In the sub-exchange Ul a switching process-is originated similar to that in exchange U2 through the operation of relay J. In a similar manner by the transmission of the next series of impulses through the contact 5|;i then according to the further operation of relay J in U2, the relay corresponding to J in the sub-exchange U2 is operated, which sets the line selector LWI (Fig. 1) on the terminals of the desired subscribers lines. If the test relay of the line selector LWI finds the desired sub- Scriber free then calling current is sent to him in known manner. l

During this time the switching process in subeXchange U| corresponds to that which went on before it in sub-exchange U2.

Since the switching arrangements of the selector pair in the sub-exchange UI apart from the auxiliary selector EW, which is not available here, are the same as for the sub-exchange U2 they are shown by Fig. 2.

When the called subscriber replies a relay corresponding to relay Y in the sub-exchange UI is energized from the subscribers loop and over a Contact corresponding to y places battery potential to thewire b2 so that in the subexchange U2 over this wire and the wiper b of selector EW relay Y is operated which, at contact ly applies battery potential to the Wire bo and in this way announces to the main eX- change HA that the subscriber has replied. The operator now withdraws the plug from the jack and relay J in sub-exchange U2 becomes deenergized. The closure of contact 837 Venergizes relays V and VI via: earth, battery, relays V and Vl, contacts 85s, 83j, 8c, earth. By closure of contact 82o relay C becomes short-circuited so that through opening of the contact 800, relay Cl, V and V| are deenergized.

At the opening of contact 940| relays P| and TI and by the opening of contact |||t|, relay U, all release.

At the closure of contact 'Mpl results, in known manner, the release of line selector LW, while the auxiliary selector EW stays in the position in which it was set for building up the connection.

During the time which lies between the opening of the shaft Contact 357clw and the closure of the shaft contact wlw of the line selector LW, relays G and PO are without current so that the line ao/ bo leading to the main exchange becomes free. The call iinder AS by opening of the contact 640| and the second deenergization of relay P becomes free for a furthercall. Simultaneously relays R and T are deprived of current.

Since, in the subexchange Ul, the opening of contact 5|g' in sub-exchange U2 also breaks the circuit for the relay U| corresponding to relay J in U2, this also releases so that via a contact corresponding to contact 83j, a relay corresponding to relay V is energized. Since in Ul a relay corresponding to relay S is, on the subscriber replying, energized over a Contact corresponding to contact 24g and held over another contact corresponding to contact 23s, further switching processes are not initiated so that in U| the selector pair consisting of line finder ASI and the line selector LWI remain busy. These are only released when the conversation is ended.

From the foregoing description it will be seen that by the transmission of a current pulse train by means of which a junction line is designated, the line selector is lifted to a level to which the junctions for this direction are connected. At the termination of this pulse train, the line selector rotates automatically. If the call is a revertive one, the line selector LW is held on the first contact of the level which is marked by the call finder AS. The auxiliary selector EW sets itself upon the line which passes via the wiper e. After this the wipers a and b of the auxiliary selector are taken to the talking wires via wipers a and b of the line selector LW.

The auxiliary selector can also be arranged so that it is not connected to the line selector Wipers but is in series with these in that all the rst contacts of the junction line level in the talking circuit banks are connected to one another and to the wipers a and b of EW.

A revertive call is then eiected in the same way as above in that the line selector after it has been positioned on the first contact of the selector EW runs on until it reaches the contacts marked by the call finder AS and switches the connection through over its Wipers.

If the line selector LW, on receipt of a designating digit, is positioned on the terminals of another sub-exchange, say U3, then after the vertical motion there is, in the same way, an automatic hunting process.

The line selector does not come to rest on the first contact of the third level since its Wiper c does not iind this contact marked by wiper d of call nder AS but by operation of its rotary magnet alternately with Winding II of relay R| (contacts '|314 and lllld) is moved on until its test relay P| finds a free line, say cl3/b3, to the sub-exchange U3. The following circuit is then formed: earth, battery, the relay corresponding to the relay T, a contact corresponding to the contact 8T, test wiper c3, wiper c of the line selector LW, windings I and I of relay P|, contacts 890|, Slis, h, Qllcl, earth.

At the opening of contact "Mpl, LW stops on this line and through switching is eiected via contacts 861m and Elpl. The remainder of the switching process goes on in known manner.

On revertive calls in the called sub-office group, by the operation of the line selector which corresponds to the position of its call finder, the line selector steps on the rst contact of the designated level and sets its auxiliary selector in operation which, in dependence on the already positioned call finder resulting from the line seized by the call, while, on the contrary, by selection of other traffic directions dependent upon the usual test processes from the line selector, a free junction in the desired direction is sought.

What is claimed is: I f

l. In a telephone vor like system, va -plurality of lines two switches -having access in vcommon to said line,s,'mea-`ns for seizing'one of said switches and transmitting thereto trains of impulses, said one switch responsive to lsaid impulses either to seize one of said lines `or to cause the other of said switches, instead of said one switch, to seize one of said lines, depending upon the number of impulses in said train.

2. In a telephone or like system, a plurality of groups of lines, two switches having access 4in common to said groups of lines, means for seizing one of said switches and for transmitting thereto impulses designating one of said groups of lines, said one switch responsive to said impulses at times to seize a line of the designated group, and said one switch responsive to said impulses at other times to cause the other of said switches, instead of said one switch, to seize a line of the designated group.

3. In a telephone system, a plurality of groups of lines, switching apparatus including two switches having access in common to said lines, means for characterizing any one of said lines, means for thereafter transmitting to said ap-paratus impulses designating any desired one of said groups of lines, means effective whenever the designated group is the group of which `the r characterized line is one to thereupon cause one of said switches to connect with said characterized line, said last means eifective whenever the designated group is not the group of which the characterized line is one to thereupon cause the other of said switches to search for and seize an idle line in the designated group.

4. In a telephone system, an automatic switch whose wipers have access to a plurality of groups of lines, means responsive to a call on any of said lines for marking in said switch the group of which the calling line is one, means for thereafter directively operating said switch to cause its wipers to search for a free line in a desired one of said groups, and means preventing said wipers from performing said search whenever said desired group is the one marked in said switch.

5. In a telephone system, an automatic switch having access to a plurality of -groups of lines, means responsive to a call on any of said lines for extending a connection from the calling line to said switch, means for thereafter directively operating said switch to cause same to search for and seize an idle line in any group except the group of which said calling line is one, and means for preventing said switch from performing said search if directively operated to the group of which said calling line is one.

6. In a telephone system, an automatic switch having access to a plurality of groups of lines, means responsive to a call on any of said lines for extending a connection from the calling line to said switch, means for thereafter directively operating said switch to cause same to search for and seize an idle line in any group except the group of which said calling line is one, means for preventing said switch from performing said search if directively operated to the group of which the calling line is one, and a second switchoperated only if said first switch is directively operated to the group of which the calling line is one to Search for and seize said calling line.

'E'. In a telephone system, a plurality of groups of lines, a link circuit, a finder switch in said link effective responsive to a call on any of said 1ines to seize the calling line, means forthereafter transmitting to said link impulses designating any one of said groups of lines, a switch in said link having access to said lines and effective whenever the designated group is the groupv of which the seized line is one to search for and connect with said seized line, and another switch in said link also having access to said lines and effective whenever the designated line is not the group of which the seized line is one to search for and seize an idle line in the designated group. 8. In a telephone system, a plurality of groups Vof lines, .a link circuit including a numerical switch and a non-numerical switch both having access to said lines, said non-numerical switch responsive to a call on any of said lines to seize the calling line and to characterize, in said numerical switch, the group of which the calling line is one, means for thereafter directively op'- erating said numerical switch to cause s-ame to search for an idle line in a desired group, means voperated if said desired group is the group characterized to preve'nt said numerical switch from performing said search,- and an auxiliary switch in said link having access to said lines and controlled by said last means only if the desired group is the group characterized to search for vand connect with the calling line. 1 Y

9. In a Vtelephone system, a two-motion switch, lines terminating in different levels of the con'- rtact bank Vof said switch, means responsive to a call on any of said lines for characterizing the level in which said line terminates, means for thereafter directively operating the wipers of said switch to any desired level, said wipers normally effective thereupon to search for an idle line in the desired level, and means preventing said wipers from performing said search if said desired level is the one characterized.

10. In a telephone system, a main exchange, a sub-exchange, a tandem exchange, means controlled by the initiation of a call by a subscriber in the sub-exchange for extending a connection from the sub-exchange to the main exchange through said tandem exchange, means for thereafter transmitting impulses over said connection from the main exchange to the tandem exchange to control the extension of the call to a desired line, a switch in said tandem exchange inoperative if -said desired line terminates in said tandem exchange, means for operating said switch to seize said connection if said desired line terminates in said sub-exchange, and switching apparatus in the sub-exchange thereafter controlled over said connection and said switch from the main exchange to complete, the call to the desired line.

1l. In a telephone system, a first exchange and a second exchange connected by trunk lines, means controlled by the initiation of a call by a subscriber in the iirstexchange for extending a connection from the first exchange to the second exchange over one of said trunk lines, a switch in said second exchange thereafter operated only if it is desired that the call terminate in said rst exchange, said switch effective at said times to automatically connect with said one trunk line, and means for transmitting impulses over said switch and said one trunk line to control switching apparatus in said iirst exchange to complete the connection.

12. In a telephone system, a vfirst exchange, a second exchange, means controlled by the initiation of a call by a subscriber in the first exchange for extending a connection from the iirst exchange to the second exchange, means :for at times further extending said connection to a called line in the second exchange, a switch in said second exchange non-operative at said times, means for at other times controlling said switch to seize said connection, and means for transmitting impulses over said switch and said connection to said iirst exchange at said other times to control the completion of the call to a called line in the first exchange.

13. In a telephone system, a first exchange, a second exchange, means controlled by the initiation of a call by a subscriber in the first exchange for extending a connection from the first exchange to the second exchange through one or more tandem exchanges, means for at times further extending said connection to a called line in the second exchange, a switch in said second exchange non-operative at said times, means for at other times controlling said switch to seize said connection, and means for transmitting impulses over said switch and said connection at said other times to control the completion of said call to one of said tandem exchanges.

14. In a telephone system, a irst exchange, a second exchange, means responsive to the initiation of a call by a subscriber in said iirst exchange for extending a connection from said rst exchange to said second exchange over a route containing one or more serially connected trunk lines, means for at times further extending said connection to a called line terminating either in said second exchange or in a distant exchange which does not lie in and is not reached over said route, a switch in said second exchange nonoperative at said times, means for operating said switch at other times to connect with the trunk line incoming to said second exchange over which said connection was extended to said second exchange, and means for transmitting impulses over said switch and said incoming trunk line at said other times to control the extension of said connection to a called line terminating either in said rst exchange or in an exchange which lies in or is reached over said route.

15. In a telephone or like system, switching apparatus, two seizing paths for said apparatus, means for seizing said apparatus over one of said paths at times and transmitting thereto a certain impulse code, means for seizing said apparatus over the other of said paths at other times and transmitting thereto the same impulse code, a plurality of lines, two switches in said apparatus each having access to all of said lines, and means for causing one of said switches to seize one of said lines in response to said code if the apparatus was seized over said one path and causing the other of said switches to seize one of said lines in response to said code if the apparatus was seized over said other path.

EDUARD WOCHINGER. 

